Process for preparing photographic elements



United States Patent Office 3,533,793 Patented Oct. 13, 1970 3,533,793 PROCESS FOR PREPARING PHOTOGRAPHIC ELEMENTS Thomas E. Whiteley, Rochester, N. assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 2, 1967, Ser. No. 619,918 Int. Cl. G03c 1/04, 1 74 US. Cl. 96-67 12 Claims ABSTRACT OF THE DISCLOSURE A process for quick drying a "gelatino, silver halide photographic emulsion wherein the halide of said silver halide is predominantly bromide, said process comprises combining a liquid gelatino emulsion of said silver halide with a synthetic polymeric binder which is compatible with gelatin and which has a glass transition temperature of less than 20 C., and removing substantially all liquid from said emulsion in less than about six minutes. Typical synthetic polymers useful in the invention are copolymers of ethylenically unsaturated monomers such copolymers containing units of alkyl acrylates and the like.

This invention relates to processes for drying photographic, gelatino, silver halide emulsions. In one aspect this invention relates to a process of decreasing the drying time of a silver halide emulsion' without increasing the fog inherent in many silver halide gelatin emulsions when quickly dried. In another aspect this invention relates to a process for quick drying a gelatino, silver halide emulsion without a substantial increase in fog by combining at least by weight based on the total binder vehicle, of a synthetic polymer with said emulsion and then removing liquid from the emulsion.

Photographic manufacturers are constantly seeking faster methods for coating and drying photographic emulsions. However, faster coating and drying procedures are accompanied by a serious fog buildup in the coated product. This problem is especially prevalent in high-speed silver halide emulsions in which the halide is predominantly bromide. When silver halide emulsions containing gelatin as the sole silver halide vehicle are rapidly dried after coating, the fast shrinkage of the gelatin apparently causes pressure on the silver halide grains which produces anover-all fog upon chemical development.

In some prior art emulsions the gelatin content has been reduced in an attempt to achieve rapid drying after coating and quick drying after processing. However, this procedure also results in a higher level of over-all fog as a high strain is apparently put on the respective silver halide grains.

Therefore, it is an object of this invention to provide a new process for making a photographic element.

It is another object of this invention to provide a process for producing a photographic film which can be dried in less than about 6 minutes without resulting in a high over-all fog.

It is another object of this invention to provide a process for increasing the drying rate of silver halide emulsion coatings without producing a high over-all fog.

It is a further object of this invention to provide a novel method for quick drying a high-speed chemically sensitized silver halide emulsion in which the halide is predominantly bromide.

These and other objects of this invention are accomplished by adding a synthetic polymer to the silver halide emulsion followed by rapid removal of the liquid carrier. The additiori of the non-gelatin vehicles of the present invention apparently allows the coated layer to be dried rapidly without severely stressing the silver halide grains. Whereas drying times with an emulsion having gelatin as the sole binder vehicle could not be less than 6 minutes without considerable fogging of the emulsion, it has now been found that drying times of much less than 6 minutes can be used without obtaining substantial fogging of a high-speed emulsion. The synthetic polymers which can be added according to the invention are compatible with gelatin and generally have glass transition temperatures of less than 20 C. Particularly good synthetic polymers are latex type compositions which are quite insoluble in water. In particular, the alkyl acrylates and copolymers thereof provide good results in this process.

In one embodiment of the process, a synthetic polymer is added to a silver halide emulsion. The resulting emulsion can be set by a chilling or by chemical setting, such as disclosed in Jones US. Pat. 2,652,345 issued Sept. 15, 1953. The emulsion layer is then subjected to conditions such as Warm air blasts of sufficient temperature and velocity to rapidly dry the emulsion layer in less than 6 minutes and preferably in 4 /2 minutes or less. The emulsion layer is considered dry when substantially all of the carrier liquid has been removed, i.e. about 15% or less carrier liquid in the emulsion. In essence, the gelatino emulsion! is dry when it contains less than about 15% moisture by weight, based on the total emulsion; it is then no longer tacky and can be easily handled without damaging the emulsion layer. The emulsion is generally not dried to eliminate all moisture as it would prohibit subsequent liquid diffusion in the chemical development steps.

The process finds particular use in drying silver halide emulsions in which the halide is predominantly bromide,

i.e., at least 50 mole percent bromide. In the preferred embodiments of the invention, the emulsions contain silver halides in which the halide is at least bromide; in particular chemically sensitized silver bromoiodide emulsions are preferred in the process. The preferred emulsions of the process can be generally characterized as being high-speed emulsions and in the preferred embodiments the process is used for drying high-speed negative films, reversal films, medical X-ray films, and the like. Generally, these emulsions can be sensitized with selenium, sulfur, tellurium, and the like, either alone or in combination with noble metal sensitizers such as gold salts or gold compounds.

A wide variety of synthetic polymers can be used in the process. Generally the polymers are copolymers of ethylenically unsaturated monomers, said polymers being compatible with gelatin and having a glass transition temperature (Tg) of less than 20 C. (Tg can be calculated by differential thermal analysis as disclosed in Techniques and Methods of Polymer Evaluation, vol. 1, Marcel Dekker Inc., NY. 1966). Particularly good polymers for use with silver bromide emulsions are the latex polymers which are relatively insoluble in Water. However, solution polymers which are more soluble in water do allow fast drying times without the fog buildup associated with an all gelatin vehicle in the emulsion.

The non-gelatin vehicles or synthetic polymers added to the emulsion according to this invention comprise co polymers having units of alkyl acrylates. Specific alkyl acrylates which may be used in making the copolymers are methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylates (e.g., n-butyl or t-butyl acrylate), amyl acrylates, hexyl acrylates and the like. Alkyl acrylate copolymers containing units of acrylic acid are especially useful in the process. Typical polymers of this type are copoly(butyl acrylate-acrylic acid), copoly(methyl acrylate-acrylic acid), copoly(ethyl acrylate-acrylic acid), and the like. In the preferred embodiment the copolymer comprises less than 30 mole percent acrylic acid; especially good results are obtained with latex alkyl acrylate copolymers having less than mole percent acrylic acid.

Alkyl acrylates having units of sulfoester acrylates are also very useful in this invention. Typical polymers of this type are copoly(methyl acrylate-sulfopropylacrylate), copoly(ethyl acrylate-sulfopropyl acrylate) and the like. In this embodiment good results are likewise obtained when the copolymer comprises less than 30 mole percent sulfoester units and preferably less than 20 mole percent sulfoester units.

In another preferred embodiment of this invention, the above-mentioned copolymers contain units of a third monomer. Exceptionally good results are obtained in the process of this invention when the synthetic polymers comprise units of (1) alkyl acrylates, (2) acrylic acid or sulfoester acrylates, and (3) an acrylic monomer unit having active methylene groups in side chains such as in malonic ester groups, acetoacetic ester groups, cyanoacetic ester groups or 1,3-diketone groups. Typical polymers of this class include copoly(ethyl acrylateacrylic acid 2 acetoacetoxy ethyl methacrylate), copoly(butylacrylate-sodium acryloxy propane sulfonate- 2-acetoacetoxyethyl methacrylate), copoly(methyl acrylate-sodium acryloyloxypropane sulfonate 2-acetoacetoxyethyl methacrylate), copoly(butyl acrylate-acrylic acid 2 cyanoacetoxyethyl methacrylate) and the like. The copolymers of (1) alkyl acrylates and (2) acrylic acid or the sulfoester can also contain units of (3) sulfobetaines. Typical copolymers having sulfobctaine units include copoly(butyl acrylate-acrylic acid-4,4,9-trimethyl-8-oxo 7 oxa 4 azonia-9-decene-l-sulfonate), and the like.

The synthetic polymer generally comprises at least 10 percent and to about 99 percent of the binder vehicle for the emulsion. In the preferred embodiments the binder vehicle for the emulsion comprises from about percent to about 75 percent synthetic polymer and from about 75 percent to about 25 percent gelatin by weight of the total binder. Generally the emulsion comprises less than 100 grams of gelatin per mole of silver halide in the emulsion. Preferably the emulsion comprises less than 75 grams of gelatin per mole of silver halide.

The light-sensitive compositions described herein can be coated on a wide variety of supports in practicing this invention. The photographic silver halide grains can be coated on one or both sides of the support which is preferably transparent and/or flexible. Typical continuous supporting sheets include, for example, cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and other polyester film as well as glass, paper, metal, wood, and the like. Supports such as paper can be coated with alpha-olefin polymers, particularly polymers of alphaolefins Containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylenebutene copolymers, and the like.

The silver halide layers and any other hydrophilic colloid containing layers present in the elements of this invention can be hardened with any suitable hardener,

including aldehyde hardeners such as formaldehyde and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides, such as oxy starch or oxy plant gums, and the like. The silver halide layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, plasticizers, and the like. The silver halide layers described herein can also contain spectral sensitizing dyes. Suitable spectral sensitizers of this type include the cyanines, merocyanines, complex(trinuclear)cyanines, complex(trinuclear)merocyanines, styryls and hemicyanines. The silver halide layers can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

It is sometimes advantageous to employ surface active agents or compatible mixtures of such agents in the preparation of the photographic materials described herein. Suitable agents of this type include non-ionic, ionic and amphoteric types, as exemplified by polyoxyalkylene derivatives, amphoteric amino acid dispersing agents, including sulfobetaines, and the like. Such surface active agents are described in US. Pat. 2,600,831 issued June 17, 1952; US. Pat, 2,271,622, issued Feb. 3, 1942; US. Pat. 2,271,623, issued Feb. 3, 1942; US. Pat. 2,275,727, issued Mar. 10, 1942; US. Pat. 2,787,- 604, issued Apr. 2, 1957; US. Pat. 2,816,920, issued Dec. 17, 1957; US. Pat. 2,739,891, issued Mar. 27, 1956 and Belgian Pat. 652,862.

The emulsion can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including for example, stabilizers or antifoggants, particularly the water-soluble inorganic acid salts of cadmium, cobalt, manganese and zinc as disclosed in US. Pat. 2,829,404, the substituted triazaindolizines as disclosed in US. Pats. 2,444,605 and 2,444,- 607, speed increasing materials, absorbing dyes, plasticizers and the like. Sensitizers which give particularly good results in the photographic compositions disclosed herein are the alkylene oxide polymers which can be employed alone or in combination with other materials, such as quaternary ammonium salts, as disclosed in US. Pat. 2,886,437 or with mercury compounds and nitrogen containing compounds as disclosed in US. Pat. 2,751,299.

The process of the invention may be used with multilayer coatings such as emulsion layers designed for color processing, for example, emulsions containing color forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials.

The photographic elements prepared according to the instant invention can be used in various kinds of photographic systems. In addition to being useful in X-ray and other non-optically sensitized systems, they can also be used in orthochromatic, panchromatic and infrared sensitive systems.

The invention can be further illustrated by the following examples of preferred embodiments thereof, although it will be understood that the examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLE I An aqueous emulsion containing 68 grams of the latex copolymer (butyl acrylate-sodium acryloylpropane sulfonate-Z-acetoacetoxyethyl methacrylate) having a Tg between -20 and 30 C. is added to a coarse-grained sulfur-gold sensitized silver 'bromoiodide photographic, X-ray emulsion (98.5 mole percent bromide and 1.5 mole percent iodide), containing 68 grams of gelatin and one mole of silver halide. The resultant emulsion is coated on both sides of a poly(ethyleneterephthalate) support at 525 mg. of silver/ft. A control emulsion containing 139 grams of gelatin per mole of silver as the only vehicle was coated in a similar manner.

One run of the control coating is dried slowly (12 minutes) and another part is dried rapidly (4 /2 minutes). The sample containing the polymer is dried rapidly 4 /2 minutes).

The dried coating were exposed of a second to a simulated X-ray screen exposure and processed in a K- dak M4 X-Omat Processor with the following results:

Drying time after coating, Rel. Sample min. speed Fog Control 12 100 04 Do 4% 102 09 Emulsion with added polymer 4% 87 03 In contrast, a silver chlorobromide (95 mole percent chloride and mole percent bromide) combined with the same polymer does not result in a similar improvement in background fog when dried in 4 /2 minutes.

Similar results are obtained when the total emulsion vehicle contains 25 percent, 40 percent, and 70 percent of the butyl acrylate-sodium acryloyloxypropane sulfonate-Z-acetoacetoxyethyl methacrylate.

EXAMPLE II A sulfur-gold sensitized silver bromoiodide emulsion (98.5 percent bromide and 1.5 percent iodide) containing 50 grams of gelatin per mole of silver halide is mixed with an emulsion containing 50 grams of copoly(butyl acrylate-2-sodiumacryloyloxy propane sulfonate-Z-acetoacetoxyethyl methacrylate) having a Tg between 20 C. and 30 C. The resultant emulsion and a control sample are coated and tested as in Example I.

Drying time after coating, Rel. Sample min. speed Fog Control. 12 100 04 Do 4% 102 09 Emulsion with added polymer 4% 118 05 Similar results are obtained when latex copolymers such as copoly(butyl acrylate-acrylic acid-2-acet0acet0xyethyl methacrylate), copoly(butyl acrylate-acrylic acid- 4,4,'9 trimethyl 8-oxo-7-oxa-4-azonia 9-decene-1-sulfonate) and copoly(butyl acrylate-acrylic acid-Z-cyanoacetoxy-ethyl methacrylate) which has glass transition temperatures less than 10 C. are added to the emulsion.

EXAMPLE III Fifty-five grams of a solution polymer of copoly(ethyl acrylate-acrylic aeid-Z-acetoacetoxyethyl methacrylate) having a Tg between 0 C. and l0 C. is added to a silver bromoiodide emulsion containing 55 grams of gelatin per mole of silverhalide. The resultant emulsion and a control emulsion are tested as described in Example I.

Drying time, Rel. Sample min. speed Fog Control- 12 100 0 D0 4% 102 O Emulsion with added polymer 4% 94 05 as described hereinabove and as defined in the appended claims.

I claim:

1. In a process for coating and drying a photographic silver halide emulsion on a support, the improvement which comprises (1) combining a liquid photographic silver halide emulsion comprising silver halide and a binder vehicle consisting essentially of about 75 to about 25 percent by weight of gelatin with about 25 to about 75 percent by weight, based on total binder vehicle, of a water-insoluble synthetic polymeric latex binder which is compatible with gelatin and which has a glass transition temperature of less than 20 C., said latex binder comprising a copolymer containing units of alkyl acrylate and units of at least a second component selected from acrylic acid, sulfoester acrylates, sulfobetaine units and units of a monomer having an active methylene group, the halide of said silver halide being predominantly bromide and (2) removing substantially all liquid to about 15 percent or less, total carrier from said emulsion in less than 6 minutes.

2. The improvement according to claim 1 wherein said emulsion is dried to a liquid concentration of less than about 15 percent by weight of total emulsion in less than about 6 minutes.

3. The improvement according to claim 1 wherein there is less than 100 grams of gelatin/mole of silver in said emulsion.

4. The improvement according to claim 1 wherein said emulsion is dried to a liquid concentration of less than about 15 percent by weight of total emulsion in less than about 6 rninutes while repressing the fog level substantially below an emulsion containing gelatin as the sole vehicle.

5. The improvement according to claim 1 wherein said silver halide is silver bromoiodide.

6. The improvement according to claim 1 wherein there is less than about 75 grams of gelatin per mole of silver in said emulsion.

7. The improvement according to claim 1 wherein said emulsion is dried in no more than about 4 /2 minutes.

8. The improvement according to claim 1 wherein said synthetic polymer is a copolymer containing units of alkyl acrylate and units of a monomer having an active methylene group.

9. The improvement according to claim 1 wherein said synthetic polymer is a latex copolymer of butyl acrylatesodium acryloyloxypropane sulfonate 2 acetoacetoxyethyl methacrylate.

10. The improvement according to claim 1 wherein the halide of said silver halide is at least percent bromide.

11. The improvement according to claim 1 wherein the said latex binder comprises a copolymer of at least three components containing units of alkyl acrylate and units of at least second and third components selected from units of acrylic acid, sulfoester acrylates, sulfobetaine units and units of a monomer having an active methylene group.

12. The improvement according to claim 1 wherein said synthetic polymer is a latex of copoly(ethyl acrylate acrylic acid-2-acetoacetoxyethyl methacrylate).

FOREIGN PATENTS 685,303 12/1952 Great Britain.

RONALD H. SMITH, Primary Examiner.

US. Cl. X.R. 

